During a metallurgical process, e.g. a refining process, it is important for the operator to know at any moment the correct temperature of the metal bath. Indeed, the temperature is one of the main parameters which the operator needs for drawing his conclusions about the correct evolution of such a process. The continuous knowledge of this temperature has become even more important as the temperature constitutes one of the main parameters in computer programs which allow the operator to continuously monitor and control the processes. The use of the technical data provided to the operator by those computer programs, puts him in a position to intervene in the process. Accurate data with regard to temperature may be of critical importance during certain phases of a refining process, e.g. when there is a risk for the temperature of a metal bath to fall below a minimum value. For example, in the case of a continuous casting tundish, the temperature of the steel bath must be maintained above a given minimum temperature, characteristic of the steel composition, to insure castability of the steel bath. Also, the quality of given semifinished or finished products may, in certain cases, depend on the invariability of the temperature of the steel or of the iron during the casting operation.
Presently, several methods are known which allow to measure the temperature of a liquid metal bath. A widespread method uses a movable lance which includes an exchangeable and consumable temperature sensor. The lower part of this lance is introduced intermittently into the bath in view of measuring the temperature thereof. The main disadvantage of this method lies in the fact that the device does not allow to measure the temperature in a continuous manner over the whole duration of a manufacturing or of a treatment process, usually due to the consumption of the sensor and/or of the lance. Additionally, the introduction of the lance into the reactor during the course of the process might disturb the normal evolution of the process or result in a complete consumption of the lance body if oxygen blowing is involved. For these reasons measuring of the temperature can only be achieved during a normal or intentional interruption of the treatment process.
According to another known method, it is foreseen to incorporate into the refractory lining of a metallurgical vessel a hollow casing of refractory material, the measuring head of e.g. a thermocouple, being located in the interior of this casing. Although this method allows to make continuously measurements of the temperature of a metal bath, the principal drawback of this approach lies in the fact that the normally utilized protection casings, made of conventional refractory material, have usually to sustain a heavy wear and are rapidly deteriorated, particularly in the presence of corrosive slag. For this reason measurements can only be made during a limited time period prior to the exchange of a worn device by a new one, normally during the relining of the vessel. Additionally the measurements of the temperature are liable to be falsified as a result of the uncontrolled wear of the device casings and of unprecise adjustments of the sensor part within the casing.
The aim of the present invention is to imagine a device for measuring the temperature of a metal bath, this device being free from the drawbacks of the other known measuring methods and this device allowing to make accurate measurements in a continuous manner without disturbing the running process. The measuring device according to the invention should be conceived in such a way that the risk of damage by the metal bath or by the slag is reduced and that the replacement of the exchangeable device has to be made only after prolonged time intervals, e.g. during the renewal of the refractory lining of the metallurgical vessel.